[Article in Japanese]
           Matsunaga Y, Yabe S, Taniguchi K, Nakayama M, Kurane I
           Kansenshogaku Zasshi 1999 Feb;73(2):97-103

        Japanese encephalitis (JE) cases confirmed by serological and/or
        virological tests, and clinically typical fatal JE cases have been
        collected using individual report cards in Japan since 1965. A total of
        324 confirmed cases (male: 167, female: 157) reported between 1982 and
        1996 were analyzed. Annual incidence of JE cases was less than one
        hundred cases from 1982 to 1991, and less than 10 cases after 1992. Age
        distribution of the patients was: 0-9 years old, 43 cases (13%); 10-39
        years old, 30 cases (9%); 40-69 years old, 161 cases (50%); over 70
        years old, 90 cases (29%). The highest incidence in male cases was
        observed in the age group of 50-59 years, and that in female was in
        60-69 years. Most of the patients (95%) were living in the western parts
        of Japan. No patient was reported from Okinawa, southern-most prefecture
        of Japan, and from Tohoku-Hokkaido area, northern parts of Japan. The
        date of onset were distributed from the end of July to the end of
        October, and the highest incidence was observed in the end of August.
        Prognosis of the patients were: complete recovery, 99 cases (31%);
        sequelae, 156 cases (48%); total, 56 cases (17%); unknown, 13 cases
        (4%). Vaccination histories of patients were reported as vaccinee, 4
        cases (1%); incomplete vaccinee, 14 cases (4%); non-vaccinee, 181 cases
        (56%); unknown, 125 cases (39%). Spread of JE virus in Japan has not
        been diminished as shown by the data of antibody acquisition of young
        swine in every summer in Japan. Based on these observations we conclude
        that JE vaccination has contributed to maintaining the low JE incidence
        among children in Japan.